(a) Field of the Invention
The present invention relates to a fabricating the capacitors of dynamic random access memory (DRAM) cells, and more particularly to the self-registered cylindrical capacitor of high density DRAMs.
(b) Description of the Prior Art
A DRAM cell comprises a metal-oxide-semiconductor field effect transistor (MOSFET) and capacitors which are built in a semiconductor silicon substrate. There is an electrical contact between the source of a MOSFET and the storage node of the adjacent capacitor, forming a memory cell of the DRAM device. A large number of memory cells make up the cell arrays which combine with the peripheral circuit to produce stack DRAMs.
In recent years, the sizes of the MOSFETs and capacitors have become continuously smaller so that the packing densities of these DRAM devices have increased considerably. For example, a number of semiconductor manufacturing companies in the world have already begun mass production of 16 M bit or even 64 M bit DRAMs. As the sizes of the capacitors become smaller, the capacitance values of the capacitors decrease, which reduces the signal to noise ratio of the DRAM circuits, causing performance problem. In order to maintain or even increase the value of the capacitance for smaller size capacitors, increasing the surface area of the polysilicon storage nodes or reducing the thickness of the capacitor dielectric layer is necessary.
Within the prior art, various shapes of capacitor structures have been used to address this issue. For example, U.S. Pat. No. 5,021,357 to Taguchi et al. (the entire disclosure of which is herein incorporated by reference) provides a method of fabricating a fin structure capacitor electrode. Another U.S. Pat. No. 5,278,091 to Fazen et al. (the entire disclosure of which is herein incorporated by reference) develops a process to manufacture a crown stacked capacitor structure. These capacitor structures can increase the surface area of the capacitor storage node, however the processes are too complicated to be practically employed for mass-production.
The present invention discloses a novel method of modifying the capacitor structure of high density DRAMs that further increase the surface area of the capacitor.